/*
 * Copyright (C) 2010 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.caliper.BeforeExperiment;
import com.google.caliper.Benchmark;
import com.google.caliper.Param;
import java.util.ArrayList;
import java.util.LinkedList;

/**
 * Tests the speed of iteration of different iteration methods for collections.
 *
 * @author David Richter
 */
public class IteratorBenchmark {
    @Param({"0", "1", "16", "256", "4096", "65536"})
    int size;

    // use concrete classes to remove any possible polymorphic overhead?
    Object[] array;
    ArrayList<Object> arrayList;
    LinkedList<Object> linkedList;

    @BeforeExperiment
    void setUp() {
        array = new Object[size];
        arrayList = Lists.newArrayListWithCapacity(size);
        linkedList = Lists.newLinkedList();

        for (int i = 0; i < size; i++) {
            Object value = new Object();
            array[i] = value;
            arrayList.add(value);
            linkedList.add(value);
        }
    }

    @Benchmark
    int arrayIndexed(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (int index = 0; index < size; index++) {
                sum += array[index].hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayIndexedLength(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (int index = 0; index < array.length; index++) {
                sum += array[index].hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayFor(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (Object value : array) {
                sum += value.hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayListIndexed(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (int index = 0; index < size; index++) {
                sum += arrayList.get(index).hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayListIndexedLength(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (int index = 0; index < arrayList.size(); index++) {
                sum += arrayList.get(index).hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayListFor(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (Object value : arrayList) {
                sum += value.hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int arrayListForWithHolder(int reps) {
        int[] sumHolder = {0};
        for (int i = 0; i < reps; i++) {
            for (Object value : arrayList) {
                sumHolder[0] += value.hashCode();
            }
        }
        return sumHolder[0];
    }

    @Benchmark
    int arrayListForEachWithHolder(int reps) {
        int[] sumHolder = {0};
        for (int i = 0; i < reps; i++) {
            arrayList.forEach(value -> sumHolder[0] += value.hashCode());
        }
        return sumHolder[0];
    }

    @Benchmark
    int arrayListToArrayFor(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (Object value : arrayList.toArray()) {
                sum += value.hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int linkedListFor(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (Object value : linkedList) {
                sum += value.hashCode();
            }
        }
        return sum;
    }

    @Benchmark
    int linkedListForEach(int reps) {
        int[] sumHolder = {0};
        for (int i = 0; i < reps; i++) {
            linkedList.forEach(value -> sumHolder[0] += value.hashCode());
        }
        return sumHolder[0];
    }

    @Benchmark
    int linkedListToArrayFor(int reps) {
        int sum = 0;
        for (int i = 0; i < reps; i++) {
            for (Object value : linkedList.toArray()) {
                sum += value.hashCode();
            }
        }
        return sum;
    }
}
